1. Field of the Invention
The present invention relates to an electrophotographic color image forming apparatus, such as a color laser printer, a color digital copying machine, and the like.
2. Description of the Related Art
For example, many users find that copies obtained by copying the same original using the same copying machine have different densities. In an electrophotograph, an image density drift occurs under the influence of a change or deterioration of image forming conditions due to different environmental factors and an elapse of time. It is important for a multi-level printer or a digital copying machine, as well as an analog copying machine, to suppress and stabilize the image density drift. In particular, in a color image, since the image density drift influences not only density reproducibility but also color reproducibility, a stable image density is an indispensable requirement. Therefore, in a conventional apparatus, a given allowable margin is provided to image forming materials and an image forming process itself, and image stabilization is attained by maintenance within this allowable margin.
However, the allowable margin to be provided to the image forming materials and image forming process itself is limited, and maintenance requires a great deal of labor and cost. Furthermore, the image density drift cycle is shorter than the maintenance cycle, and a stable image density cannot always be obtained entirely by maintenance.